When conducting polymerizations on a commercial basis, it is important to utilize process conditions and components which will allow the molecular weight of the end products to be narrowly and reproducibly defined. The characteristics of a given polymer and its usefulness are dependent, among other things, upon its molecular weight. Hence, it is desirable to be able to predict with some certainty the molecular weight of the end product of the polymerization. When the molecular weight is not narrowly definable, or is not reproducible on a systematic basis, the process is at a commercial disadvantage.
Further, it is desirable to produce elastomeric compounds exhibiting improved properties such as reduced hysteresis loss characteristics. Such elastomers, when compounded to form articles such as tires, power belts and the like, will show an increase in rebound, a decrease in rolling resistance and less heat build-up when mechanical stresses are applied.
A major source of hysteretic power loss has been established to be due to the section of the polymer chain from the last cross link of the vulcanizate to the end of the polymer chain. This free end cannot be involved in an efficient elastic recovery process, and as a result, any energy transmitted to this section of the cured vulcanizate is lost as heat. It is known in the art that this type of mechanism can be reduced by preparing higher molecular weight polymers which will have fewer end groups. However, this procedure is not useful because processability of the rubber with compounding ingredients and during shaping operations decreases rapidly with increasing molecular weight of the rubber.
The present invention provides polymers made by anionic initiation with novel alkyllithium compounds containing cyclic amines. Use of the compounds of the present invention allows the incorporation of a functionality from the initiator to be incorporated at least at the head of the polymer chain. The initiators used in the invention not only provide for improved polymerizations, but also result in polymers having a relatively predictable, controllable and reproducible molecular weight range distribution. Because of the incorporated functionality, the polymers and products of the invention exhibit improved (that is, reduced) hysteresis loss characteristics.
Certain aminoalkyllithium compounds are known in the art. For example, U.S. Pat. No. 4,935,471 discloses dialkylamino oligoalkenyl lithiums including piperidinyl and pyrrolidinyl oligoalkenyl lithiums. It has been found that when compounded with conventional vulcanizable rubber components, some of these materials do not interact effectively with carbon black. Others possess an odor which makes their commercial use undesirable. U.S. Pat. No. 5,496,940 teaches organolithium compounds containing a cyclic amino group. These compounds contain a lithium alkyl moiety that is bonded to the amino nitrogen. The polymers resulting from these initiators have the amino group tethered through the nitrogen.